The Islamic State (IS) group issued a statement claiming the attack, which took place late Saturday in the tribal desert province of Al-Anbar, primarily home to Sunni Muslims.

A local security official told AFP on condition of anonymity that "two suicide bombers disguised as soldiers entered the Al-Hal Party headquarters", a prominent party in the region.

One of the attackers "detonated his explosive belt while political leaders held a meeting" at the campaign headquarters in the city of Hit, about 200 kilometres (125 miles) west of Baghdad, General Qassam al-Mohammadi, head of army operations in the area, told AFP.

"Three members of the security forces were killed and seven people, including candidate Zineb Abdel Hamid al-Hiti, were wounded," he said.

A municipal employee on Sunday also succumbed to injuries sustained in the attack, the anonymous official said.

He said the second attacker detonated his belt shortly after the first, but did not cause any casualties.

Medical sources confirmed the death toll of four and said candidate Hiti had been hospitalised with light injuries.

Sunnis are a minority in Iraq, where more than two-thirds of the population is Shiite Muslim.

For three years, the Sunni jihadist group IS ruled the province, which stretches from the western periphery of the capital to the border with war-torn Syria.

In December, Baghdad declared "victory" against IS after retaking the group's last urban stronghold in Al-Anbar.

But according to experts, jihadists are still hiding along the porous border with Syria and in parts of the Iraqi desert.

Elections held in Iraq since the US-led invasion in 2003 and the fall of Saddam Hussein's regime have all been marred by deadly violence.

But in the runup to the May 12 polls, the country has enjoyed a respite from violence.